Some motion detecting devices use a pair of sensing elements as a magnetoresistive unit, as disclosed in U.S. Pat. No. 5,359,287, to detect rotation of a disk-shaped magnetized rotor in response to the magnetism generated from a biasing magnet disposed to face the magnetized rotor. The sensing elements are arranged to be inclined 45° relative to a line of symmetry that corresponds to a radial center line of the magnetized rotor. This line corresponds to the magnetic center of the biasing magnet. According to this arrangement, the magnetic flux generated by the biasing magnet and passing through the magnetoresistive unit deflects on a plane parallel with the side circular plane of the magnetized rotor, when the magnetized rotor rotates. This deflection is used to detect rotation of the rotor.
It sometimes becomes necessary to change the arrangement of the magnetoresistive unit relative to the biasing magnet for improving performance of the device. If the magnetoresistive unit is displaced sidewise in parallel so that the line of symmetry of the magnetoresistive unit is parallel with the radial center line passing through the magnetic center of the biasing magnet and the center of rotation of the magnetized rotor, the output of the magnetoresistive unit changes largely in correspondence with temperatures under which the magnetoresistive unit operates. This large temperature dependent characteristics of the magnetoresistive unit requires different threshold levels for respective temperatures in shaping or digitizing the output signal of the magnetoresistive unit into a pulse signal.